Gypsy moth

The European Gypsy Moth (EGM) (Lymantria dispar dispar) is a non-native, invasive forest pest that was introduced to North America from Europe in 1869. It was first detected in Ontario in 1969 and has quickly spread across southern Ontario during the 1980’s. EGM is unfortunately considered a well-established regional pest in southern Ontario.

A single EGM caterpillar can eat an average of one square metre of leaves.

The City is taking an Integrated Pest Management (IPM) approach. This means we are using different management techniques to address the pest population starting with the least harmful to the environment. 

You can take action to remove EGMs in winter, prior to eggs hatching in spring.  Removing and destroying egg masses in winter reduces the number of hatched caterpillars in spring.  Likewise, trapping and destroying both female and male moths in summer reduces the number of moths who then breed and start the egg laying cycle again. 

The earlier and more often the pest’s life cycle can be interrupted, the more successful we will be in managing the pest.

 

EGM life cycle

Image
Infographic on the gypsy moth lifecycle. For more information on this infographic please contact forestry@london.ca

Trapping tips

May to July: hand pick caterpillars (small trees, shrubs and plants)

Gently shake  so caterpillars fall from leaves. Thoroughly inspect the remaining foliage, branches and trunk for caterpillars and, using gloves, pick them off. Fallen and collected caterpillars should be placed and left to soak in soapy water for a few days, then dispose of the contents.

What to Look For:

The caterpillars of the gypsy moth are dark and hairy. They have five blue dot pairs and six red dot pairs on their back. They go through 4-5 "molting" events where they shed their skin and each time, they get bigger.

Image
Gypsy Moth caterpillar on leaf
Photo courtesy of  Ontario's Invading Species Program
July to August (large caterpillar stage): burlap banding

Once the caterpillars grow to about 2.5 cm (an inch) in length by mid-June, they will move down the trunk. Reduce the number of larvae on the trees in your yard by trapping them.

  1. Wrap and secure a piece of burlap cloth around the stem/trunk of your tree
  2. Tie twine or rope around the center or slightly below the center of the burlap
  3. Drape the burlap cloth over the twine or rope so there is an overhang where the caterpillars can crawl underneath to seek shelter during the day
  4. Check the trap by lifting the overhanging burlap cloth every afternoon and collect any hiding caterpillars
  5. Put them into a bucket of soapy water for a few days to destroy them, then dispose of the contents
July to August (female moth stage): burlap wrapping

Similar to the large caterpillar stage, to trap female moths (which are unable to fly) wrap burlap lower on the trunk of the tree to trap the moth before it crawls up the tree and lays eggs. Once captured, put the moths in a container of soapy water and leave them there for a few days, then dispose of the contents.

July to August (male moth stage)– trap male moths

Hang non-toxic pheromone baited traps (available at hardware and nature stores) in trees to attract male moths. The scent draws the male moth and the trap then prevents them from mating with female moths and producing eggs. Once captured, put the moths in a container of soapy water and leave them there for a few days, then dispose of the contents.

November to late April (egg stage) – destroy egg masses

Survey your property for egg masses and scrape them off surfaces into soapy water to destroy them.

  1. Place a container below the egg mass
  2. Use a scraper tool to remove the egg mass from the surface. Ensure that all eggs are scraped. Try not to leave any residual eggs in bark ridges or crevices
  3. Empty the contents of your catchment container or bag into a bucket of soapy water
  4. Leave the eggs sitting in the bucket for a day or two, then dispose of the contents

Frequently asked questions

What kinds of trees are most affected by the EGM caterpillar?

EGM prefers the leaves of deciduous hardwood trees like maple, elm and oak. It will also feed on apple, alder, birch, poplar and willow trees. As the caterpillar matures, and population levels increase, it will also begin to attack evergreens such as pine and spruce. EGM don't appear to like ashes, sycamores, butternuts, black walnuts and dogwoods.

How much damage can EGM cause to trees?

Tree damage depends on the degree of infestation, past defoliations, the tree's vulnerability and the environment and can range from light to almost complete defoliation. If the tree has been weakened or stressed by other conditions, and attacked repeatedly in recent years, the defoliation can result in the death of the tree.

Does the EGM have any natural enemies?

Yes. Predators include other insects like wasps, flies, beetles, ants and spiders as well as birds such as chickadees, blue jays, robins and nuthatches. Animals such as chipmunks, squirrels and raccoons will also prey on the caterpillar.

The wasp that targets the EGM is a parasite of the EGM egg. It is now commonly found wherever EGMs are and has become an important natural control of the EGM.

Also, the EGM is susceptible to several naturally occurring diseases caused by bacteria, fungi and a virus. The virus and bacteria escalate when EGM populations peak. The EGM virus disease is often referred to as “wilt” because dead caterpillars hang in an inverted “V” from tree trunks or foliage.

These natural biological controls contribute the most to keeping levels within a normal range and tend to follow 2-3 years after the gypsy moth populations peak.

What is the City doing to help manage this invasive pest?

The City of London is responsible for managing and maintaining trees on City-owned lands: boulevard trees, trees in public parks, and Environmentally Significant Areas (ESAs).

In 2008, the City completed a comprehensive Urban Forest Effects Model (UFORE) study which noted that 13% of London's tree canopy would be susceptible to EGM.

In 2009, the City performed an aerial spray of a biological pesticide called Btk for EGM management. It was applied to a few City-owned parks and an environmentally significant area, not over private property. These locations were targeted for having high infected oak tree populations, combined with a several year drought in the area, which compounded tree decline and death.

Since 2009, the City has taken an Integrated Pest Management (IPM) approach. This means we are using different management techniques to address the pest population starting with the least harmful to the environment.

In early 2020, City crews removed egg masses from City trees located on boulevards, parks and Environmentally Significant Areas.

Now, in 2021, after seeking public feedback in January, Urban Forestry is taking a recommendation on managing Gypsy Moths to the Planning & Environment Committee in mid-February.

What can residents do?

Property owners are responsible for managing trees (and pests) on their property. You are encouraged to monitor trees on your property - look for egg masses in winter, caterpillars in spring, and moths in July and August - and take action to remove EGMs as often as possible.

Should property owners consider a commercial insecticide to help control the EGM population?

During severe infestation an insecticide may be considered a viable option. Homeowners can consider consulting with, and hiring a licensed contractor to apply pesticide sprays or tree injections. Timing of the application and the treatment of the entire canopy is essential to the success of control. You should also be aware that pesticide applications do not produce an instant defense and will not completely eradicate the problem, but can be very effective in reducing the insect population when used appropriately.

Why are there still some egg masses on boulevard trees, after the City has been by?

Our arborists have worked to remove the egg masses from City trees to reduce the population. It is not possible to eliminate this pest completely as it is well established in our region.  Our overall objective is to reduce numbers. We continue to monitor numbers and will take further action if deemed necessary.

My family has been experiencing rashes that we think come from EGM caterpillars. What should we do about this?

The hairs of the EGM contain histamine which some people are allergic to. Not everyone will have a reaction if coming in contact with the caterpillar, but it is possible and is a known adverse effect. If you are experiencing any sort of reaction, please contact your family care physician for medical advice.

Why hasn't the City done a broad aerial spray to manage EGMs? Will it happen?

Other regions or cities may spray if they continue to experience widespread and severe amounts of gypsy moth damage. The City of London’s current status with EGM is that it is isolated to two pockets that are being monitored. With EGMs primarily located in a small portion of the City, management must also keep cost prohibitions in mind.

At this time, the City is considering our EGM management approach for 2021.  Urban Forestry will be taking a recommendation to the Planning and Environment Committee in mid-February.

Important Links

Invasive Species Centre | Forest Invasives | Ontario's Invading Species Program | Government of Ontario | Canadian Food Inspection Agency (CFIA)

 

Last modified:Wednesday, February 03, 2021